1. Field of the Invention
The present invention relates to a cooling type photodetector in which at least a cooling device is built inside a housing for accommodating a photoelectric tube.
2. Related Background Art
A cooling type photodetector of this kind is disclosed, for example, in Japanese Patent Laid-Open No. 6-88747 (Reference 1), which describes the configuration of a cooling type photodetector comprising a cooling device composed of a Peltier element, and an annular cooling block attached to the low temperature side (heat absorbing portion) of the cooling device, both being built inside a box for accommodating a photomultiplier. Further, Japanese Patent Laid-Open No. 5-312638 (Reference 2) discloses the configuration of an infrared optical apparatus comprising an infrared image detector, a cooling device composed of a Peltier element, and a cooling framework attached to the heat absorbing side (heat absorbing portion) of the cooling device, all being built inside a lens barrel of an optical system for forming an infrared image.
In the the cooling type photodetector described in Reference 1, the annular cooling block surrounds and cools down one end portion on the photoelectric surface side of a photomultiplier and one end portion of a vacuum cell type light entrance window facing the photomultiplier. The portion of the photomultiplier other than the one end portion is supported within the box via a heat insulating material, and the other end portion of the vacuum cell type light entrance window is supported such as to be fitted into a wall portion of the box. Then, the other end portion of the vacuum cell type light entrance window is heated through the wall portion of the box by a heat radiating plate to which a high temperature side (heat radiating portion) of the cooling device is attached.
On the other hand, in the infrared optical apparatus described in Reference 2, an auxiliary lens of the optical system is solely supported on the cooling framework so as to be cooled down. The infrared image detector is cooled down through a holding portion by another cooling portion filled with liquid nitrogen or the like.
The inventors have studied conventional photodetectors in detail and, and as a result, have found problems as follows. Namely, in the cooling type photodetector described in Reference 1, the annular cooling block surrounds and cools down indirectly the one end portion on the photoelectric surface side of the photomultiplier. This causes a poor cooling efficiency, and hence has a possibility that the occurrence of noise is not sufficiently suppressed in the photomultiplier. Further, the vacuum cell type light entrance window that is heated generates background light (thermal radiation), so that the background light is incident on the photomultiplier and can increase the dark current of the photomultiplier. This creates drawbacks in precision detection of weak light.
On the other hand, the infrared optical apparatus described in Reference 2 needs two separate systems of cooling means constituted by the cooling means comprising the cooling portion and the retaining portion for cooling the infrared image detector, and the auxiliary cooling means having the cooling device and the cooling framework for cooling the auxiliary lens of the optical system. This creates drawbacks in the size reduction of the apparatus configuration.
The invention has been devised in order to resolve these problems. An object of the invention is to provide a photodetector capable of detecting even weak light with precision and having a structure permitting size reduction.
The photodetector according to the present invention comprises a housing, a photoelectric tube accommodated in the housing, a heat conductive supporting member accommodated in the housing, and a cooling device accommodated in the housing and arranged between the heat conductive supporting member and an inner surface of the housing. The housing has a light entrance window for introducing light to be measured into inside thereof. The photoelectric tube has a light receiving faceplate and a photoelectric surface located on one surface of the light receiving faceplate. The heat conductive supporting member has a supporting protrusion piece for fixing the photoelectric tube, and the supporting protrusion piece has an aperture stop for introducing light to be measured, which is transmitted through the light entrance window of the housing, to the photoelectric surface of the photoelectric tube through the light receiving faceplate of the photoelectric tube. The cooling device has a heat radiating portion being in contact with the inner surface of the housing and a heat absorbing portion being in contact with the heat conductive supporting member. In particular, in the photodetector according to the present invention, it is preferable that the photoelectric tube is fixed only to the supporting protrusion piece while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop.
In this case, when the cooling device begins cooling operation, the photoelectric tube is cooled down starting from the light receiving faceplate side via the supporting protrusion piece of the heat conductive supporting member fixed to the heat absorbing portion of the cooling device. At that time, the photoelectric tube is fixed only to the supporting protrusion piece, so that heat inflow through other members is prevented. Thus, the photoelectric surface of the photoelectric tube is efficiently cooled down through the light receiving faceplate by the cooling device serving as a cooling source, so that a stable cooling temperature is obtained. This suppresses the emission of thermal electrons from the photoelectric surface of the photoelectric tube, and hence sufficiently suppresses the occurrence of noise in the photoelectric tube. In this state, light to be measured, which is transmitted through the light entrance window of the housing, is incident on the photoelectric surface of the photoelectric tube via the aperture stop of the supporting protrusion piece, while background light emitted from the housing is shielded by the supporting protrusion piece around the aperture stop so as not to be incident on the photoelectric surface.
The photodetector according to the present invention may comprises a housing, a photoelectric tube accommodated in the housing, a heat conductive supporting member accommodated in the housing, a cooling device accommodated in the housing and arranged between the heat conductive supporting member and an inner surface of the housing, and an optical system for collecting light to be measured which is transmitted through the light entrance window of the housing. The housing has a light entrance window for introducing light to be measured into inside thereof. The photoelectric tube has a light receiving faceplate and a photoelectric surface located on one surface of the light receiving faceplate. The heat conductive supporting member has a supporting protrusion piece for fixing the photoelectric tube, and the supporting protrusion piece has an aperture stop for introducing light to be measured, which is transmitted through the light entrance window of the housing, to the photoelectric surface of the photoelectric tube through the light receiving faceplate of the photoelectric tube. The cooling device has a heat radiating portion being in contact with the inner surface of the housing and a heat absorbing portion being in contact with the heat conductive supporting member. The optical system has a lens barrel located between the light entrance window of the housing and the supporting protrusion piece of the heat conductive supporting member. In particular, in the photodetector according to the present invention, it is preferable that the photoelectric tube is fixed to one surface of the supporting protrusion piece of the heat conductive supporting member while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop. Additionally, it is preferable that the lens barrel of the optical system is fixed to the other surface of the supporting protrusion piece of the heat conductive supporting member while the lens barrel of the optical system is aligned with the aperture stop.
In this case, when the cooling device begins cooling operation, the photoelectric tube is cooled down starting from the light receiving faceplate side via the supporting protrusion piece of the heat conductive supporting member fixed to the heat absorbing portion of the cooling device. At the same time, the optical system is cooled down together with the lens barrel. Thus, the photoelectric surface of the photoelectric tube is efficiently cooled down through the light receiving faceplate. This suppresses the emission of thermal electrons from the photoelectric surface, and hence sufficiently suppresses the occurrence of noise in the photoelectric tube. Further, the optical system is cooled down well, so that the generation of background light (thermal radiation) from the optical system is suppressed sufficiently. In this state, light to be measured that is transmitted through the light entrance window of the housing is collected on the photoelectric surface of the photoelectric tube via the aperture stop of the supporting protrusion piece by the optical system, while background light emitted from the housing is shielded by the supporting protrusion piece around the aperture stop so as not to be incident on the photoelectric surface.
Further, in the photodetector according to the present invention having the above-mentioned optical system, the photoelectric tube is preferably fixed only to one surface of the supporting protrusion piece of the heat conductive supporting member, while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop.
In this case, when the cooling device begins cooling operation, the photoelectric tube is cooled down starting from the light receiving faceplate side via the supporting protrusion piece of the heat conductive supporting member fixed to the heat absorbing portion of the cooling device. At the same time, the optical system is cooled down together with the lens barrel. At that time, the photoelectric tube is fixed only to the supporting protrusion piece, so that heat inflow through other members is prevented. Thus, the photoelectric surface of the photoelectric tube is efficiently cooled down through the light receiving faceplate by the cooling device serving as a cooling source, so that a stable cooling temperature is obtained. This suppresses the emission of thermal electrons from the photoelectric surface of the photoelectric tube, and hence sufficiently suppresses the occurrence of noise in the photoelectric tube. Further, the optical system is cooled down well, so that the generation of background light (thermal radiation) from the optical system is suppressed sufficiently. In this state, light to be measured that is transmitted through the light entrance window of the housing is collected on the photoelectric surface of the photoelectric tube via the aperture stop of the supporting protrusion piece by the optical system, while background light emitted from the housing is shielded by the supporting protrusion piece around the aperture stop so as not to be incident on the photoelectric surface.
In the photodetector according to the present invention which has the above-mentioned optical system, it is preferable that the photoelectric tube is fixed only to one surface of the supporting protrusion piece of the heat conductive supporting member while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop, and that the lens barrel of the optical system is fixed only to the other surface of the supporting protrusion piece of the heat conductive supporting member while the lens barrel of said optical system is aligned with the aperture stop.
In this case, when the cooling device begins cooling operation, the photoelectric tube is cooled down starting from the light receiving faceplate side via the supporting protrusion piece of the heat conductive supporting member fixed to the heat absorbing portion of the cooling device. At the same time, the optical system is cooled down together with the lens barrel. At that time, the photoelectric tube is fixed only to the supporting protrusion piece, so that heat inflow through other members is prevented. Thus, the photoelectric surface of the photoelectric tube is efficiently cooled down through the light receiving faceplate by the cooling device serving as a cooling source, so that a stable cooling temperature is obtained. This suppresses the emission of thermal electrons from the photoelectric surface of the photoelectric tube, and hence sufficiently suppresses the occurrence of noise in the photoelectric tube. Further, the optical system is fixed only to the supporting protrusion piece, so that heat inflow through other members is prevented. Thus, the optical system is efficiently cooled down by the cooling device serving as a cooling source, so that the generation of background light (thermal radiation) from the optical system is suppressed sufficiently. In this state, light to be measured that is transmitted through the light entrance window of the housing is collected on the photoelectric surface of the photoelectric tube via the aperture stop of the supporting protrusion piece by the optical system, while background light emitted from the housing is shielded by the supporting protrusion piece around the aperture stop so as not to be incident on the photoelectric surface.
In a photodetector according to the present invention, the photoelectric tube may be fixed in a state where the light receiving faceplate is in direct contact with the supporting protrusion piece, or alternatively, in a state where the light receiving faceplate is in contact with the supporting protrusion piece via an insulation plate arranged around the aperture stop. When the light receiving faceplate is in contact with the supporting protrusion piece via the insulation plate, variation in the electric potential of the light receiving faceplate is prevented so that the electric potential of the photoelectric surface is stabilized.
Since a high voltage is applied on the tube body of the photoelectric tube in some cases, it is preferable that an insulator is adhered to the periphery of the tube body of the photoelectric tube for easy handling. In particular, it is preferable that the insulator is composed of Teflon having good insulating property and a low gas release rate in vacuum.
In order to fix the photoelectric tube whose tube body is applied with a high voltage onto the supporting protrusion piece, it is preferable that a leaf spring-like stopper is supported on the supporting protrusion piece via an insulating support structure, so that the photoelectric tube is pressed against and fixed to the supporting protrusion piece by the stopper. In this case, when an insulator is adhered to the periphery of the tube bofy of the photoelectric tube, the insulation is preferably ensured doubly, together with the insulating support structure. When the insulator is composed of a tube formed of Teflon (a Teflon tube, hereafter), the stopper bites into the Teflon tube so as to preferably press securely the photoelectric tube against the supporting protrusion piece.
When the inner space of the housing is maintained in a vacuum state, heat inflow from the housing into the photoelectric tube is preferably prevented without using a heat insulating material. In this case, when the lens barrel of the optical system is provided with an opening for connecting between the inside and the outside of the lens barrel, and when the lens barrel is attached with a light shielding cover for covering the opening, the occurrence of dew condensation on the inner side surface of the condenser lens is prevented without degrading the light shielding function.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.